A technique for preparing crystallizable 3,4-polyisoprene is disclosed by Sun and Wang, 2 Acta Polymerica Sinica 145 (1988). These Chinese researchers disclose that crystalline 3,4-polyisoprene containing about 70% 3,4-microstructure and about 30% cis-1,4-microstructure can be prepared using a catalyst system containing iron acetyl acetonate, a trialkyl aluminum compound, and an amine modifier in benzene. However, the utilization of this catalyst system developed by the Chinese results in the formation of gel and poor yields.
Various catalyst systems and procedures have been used to copolymerize 1,3-butadiene and isoprene. However, such techniques typically do not result in the formation of random isoprene-butadiene rubbers which have high vinyl contents. Nevertheless, it would be desirable to employ such random isoprene-butadiene rubbers in many applications, such as tire tread compounds.